Wattmeter of the induction type



July 13 1926.

R. M. FIGHTER WATTMETER OF THE INDUCTION TYPE Filed June 1925 L Fig.3 /2

increase of the brakin PM; July s, 1926.

UNITED STATES 1,592,730 PATENT OFFICE.

RENE MABCEL FIGHTER, OF PARIS, FRANCE.

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Application filed June 22, 1925, Serial No. 38,883, and in Germany June 24, 1924.

- In electric meters of the induction type, a horizontal rotatable disc made out of a good conducting metal such as copper or aluminium is placed between a first U-shaped electromagnet provided with a winding inserted in series in the circuitof the cur rent to be measured and a second unipolar electromagnet connected in parallel with the said circult. These two electromagnets constitute what is termed the wattmeter. The magnetic lines of force passing from one pole to the other of the U-shaped series electromagnet are deflected towards the pole of the second 'electromagnet. Thereby they pass through the rotatable disc or armature wherein they cause eddy currents to arise; these create a torque which makes the disc rotate.

In the meters now used, the indications are more and more behind the real load when latter increases somewhat beyond the normal load of the meter. The reason of this is that the eddy currents which arise in the disk create a braking torque; the torque caused by the series electromagnet is proportional to the square of the field intensity of said electromagnet. This braking torque makes the driving torque decrease by a fraction rapidly increasing with the load.

The object of the present invention is to cprrect these errors by a special arrangement of the wattmeter. Besides the latter is such as can'be made cheaply.

This wattmeter is characterized by the fact that an increase of the intensity of the current beyond a certain limit causes a deyflecti on of the magnetic lines of force towards the periphery of the series electro magnet. Thus the new lines of force created are further removed from the center and the diving torque created by them acts with a longer lever arm, thereby compensating the torque. This can be provide for, for instance, by projections facing each other on the poles of the U-shaped mries electromagnet andby soft iron parts also bearing pro ections and placed near these oles on the exterior side with reference to t e center of the rotatable disc, For the limit intensity mentioned hereabove the projections on the poles of the 'electromagnet are saturated to a certain extent and when the intensity increases beyond this limit, the new lines 0 force created are deflected more towards the soft iron p rts, that is towards the periphery. Below his and there ore hardly any lines of force can pass through the outer soft iron parts. Experience shows that the indications of the meter thus devised are not wrong by more than 1% at a load double the normal load.

The electromagnet inserted 'in parallel comprises preferably a core constituted by a pile of soft iron blades. These blades should have a rectangular shape and an extension of one of the sides forms the only pole of this unipolar electromagnet. The end of the adjacent side of the rectangular core comes as near as ossible into contact with this extension. T e coil can be easily set round the side provided with the extension, by pushing aside theyielding blades constituting the. adjacent side.

By way of example a form of execution of this wattmet-er is described herein below and shown on the appended drawings.

Figures land 2 are diagrammatical side views in two perpendicular planes.

Fig. 3 is a plan view of the series electromagnet.

Fig. 4 is a plan view of the electromagnet inserted in parallel showing how the coil can be set on its core.

The disc (or armature) 1 is borne by a vertical shaft diagrammatically shown by 2.- Above the disc is the electromagnet inserted in parallel which comprises a coil of thin wire 3 and a core 4 having the shape of a rectangle radially disposed with reference to the disk and provided with only one pole 5 near the disk and removed from the center thereof. Below the disk and perpendicular to the core 4 is placed the series electromagnet comprising two coils 6 and 7 set round the U-shaped core 8. The latter ends near the disk and opposite the pole 5 with its two poles 9 and 10 each provided with a projection 9 10 Near the poles 9 and 10 and on the far side of the disk with reference to the center of the disk 1 are placed two soft iron parts 11 and 12 each provided with a projection 11, 12 pointing'towards the, corresponding pole 9, 10.

The lines of force of the'magnetic field of the series electromagnet spread out between the (Erojections 9', 10', and are attracted upwar by the pole'5 of the other electromagnet whereby they arev made to pass through the disk 1. For a certain intensity of the current, the projections 9 and 10* which have a reduced cross-section are more saturated by the magnetic, lines of force than: therastsflheara if the intensity in creases, the number of lines of force going from the poles 9, 10 towards the parts 11, 12 will also increase and as these lines are further removed from the center than the others, they will produce a-torque acting on the disk with a longer lever arm; the polar projections and the parts 11 and 12 are suitably shaped so as to provide for an automatic compensating of the braking torque created by the series electromagnet.

The core 4 of the electromagnet in parallel is 'preferabl made out of a pile of soft iron blades the s ape of which is shown on Fig. 1. Generally these cores are made in. two parts united through the joints 4' and 4". Such joints greatly increase the reluctance of the core. The core shown on Fig. 1 has only one break in the metal which is formed by the very small air-gap 4".

The reluctance is diminished enough by this suppression of the joint 4 to allow a reduction of about 20% of the weight of copper of the coil 3.

To fit the coil 3 on the side of the rectangular core ending with the pole 5it is sufiicient to push apart, as shown on Fig. 4, the ends 1314 of the yielding metal blades 15 of the adjacent side of the core.

What I claim is:

1. In a wattmeter of the induction type, the combination ofan unipolar electromagnet connected in parallel with the circuit of the current to be measured and disposed over the rotatable element of the meter, a second U-shaped electromagnet connected in series with the said circuit and disposed under said rotatable element, a soft iron part under the rotatable element near each pole of said second electromagnet and on the outside thereof with reference to the center of therotatable element, a projection borne by each soft iron part and pointing towards the corresponding 1e, and a projection on each pole of sai second electromagn'et adapted to be saturated at normal load, said latter projections being disposed opposite each other.

2. In a wattmeter ofthe induction type, the combination of an unipolar electromagnet connected in parallel with the circuit of the current to be measured, and disposed over the rotatable element of the meter, a number of metal blades of rectangular shape constituting the core of said electromagnet,

an extension of one of the sides of said core 7 forming the "pole of said electromagnet, a small air-gap being provided between said extension and the ad acent side of the core, 7 a coil on the side of the core provided with an extension, a second U-shaped electromagnet connected in series with the said circuit and disposed under said rotatable element, a soft iron part under the rotatable'element,

near each pole of said electromagnet and on the outside thereof with reference to the center of the rotatable element, a projection borne by each soft iron part and inting towards the corresponding pole, an a projection on each pole of said second electromagnet adapted to be saturated at normal load, said latter projections being disposed opposite each other.

In testimony whereof I have name to this specification.

RENE- MARCEL FIGHTER.

signed my 

